In the history of the United States, "waving the bloody shirt" refers to the practice of politicians referencing the blood of martyrs or heroes to criticize opponents.

In American history, the phrase gained popularity with a factitious incident in which Benjamin Franklin Butler of Massachusetts, when making a speech on the floor of the U.S. House of Representatives, allegedly held up a shirt stained with the blood of a carpetbagger whipped by the Ku Klux Klan. (While Butler did give a speech condemning the Klan, he never waved anyone's bloody shirt.)